My
complete and utter guess would be that it's an evolution from being a predator. I'd guess that it would be beneficial to be able to keep their head still to watch prey. I'd also guess that most birds would react the same way. My uncle is an avid bird watcher, and I've been on a few bird counts with him in the past. I've seen many birds - especially birds of prey - do very similar things when tracking food while in flight. Their heads will stay locked on a target while their bodies & wings adjust to air currents.
